Fuel for a diesel engine has wide property range, and a combustion condition is significantly varied according to the fuel property variation. Thus, due to the fuel property variation, a fuel injection period and a combustion period are varied, which causes deterioration in emission and a misfire. The combustion condition may become unstable.
JP-2006-226188A shows a fuel property detecting apparatus which detects the cetane value of the fuel based on the combustion condition of the fuel injected by a pilot injection.
However, even though the cetane value of the fuel is detected, it is likely that the deterioration in combustion condition may not be restricted by executing the combustion control according to the cetane value. For example, due to a variation in fuel composition, it is likely that a fuel combustion region is concentrated in a vicinity of an inner surface of a cylinder, so that it is likely that a cooling loss and an emission of soot may not be suppressed.